NAIADES OF MISSOURI 3 1 



(1913, p. 104) finds the host that is the specific distributor of this 

 valuable shell to be a fish known as "skipjack" (Pomolobus 

 chrysochloris). 



Genus Amblema Rafinesque. 



1820 — Amblema Rafinesque, Monograph Biv. Shells of R. Ohio. 

 1912b — Crenodonta (Schluter) Ortmann, An. Car. Mas., VIII, pp. 

 245-250. 



(Type Unio plicata [Lesneur] Say). 



Animal Characters: — Branchial opening long with few 

 small arboreal papillae; anal large, very slightly crenulated; 

 supra-anal separated from anal by very short mantle connection, 

 sometimes no connection at all ; gills large, inner wider and longer, 

 outer connected high up to mantle antero-ventrad, inner laminae 

 of inner gills free from visceral mass; palpi long, falcate united 

 most of their length antero-dorsad; marsupia occupy all four 

 gills, ovisacs of inner being wider, when gravid ovisacs expand 

 transversely; conglutinates white, compressed, leaf-like shape, 

 discharged through anal passage in rather broken or loose masses; 

 glochidia small, spineless, subovate. 



Shell Characters: — Shell subquadrate to subtrapezoidal, 

 thick, beaks more or less elevated, sculptured with concentric 

 lines slightly angled at the base of the post-umbonal ridge and 

 disappearing out upon the disk or continued there in a zigzag 

 pattern of irregular broken pustules, nodules and oblique, indu- 

 lated or plicated folds, the latter being disposed across the pos- 

 terior half; hinge teeth heavy and well developed; beak cavities 

 deep crevices under rather wide interdentum; vein markings 

 on antero-pallial margin distinct; nacre usually white. 



Miscellaneous Remarks: — It is recognized by students 

 of Naiades that this genus needs a thorough revision — especially 

 as to its shell characters. Like the genus Fusconaia, Amblema is 

 a group of all sorts of inter-grading and puzzling forms. However, 

 for this State it is not so much a question of facts regarding a 

 predominance of these plicated forms for the different faunae as 

 it is an application of these varieties to the present chaotic no- 

 menclature for this genus. As nearly as the writer is able to 

 determine, after a correspondence with students and a thorough 

 study of literature and actual field conditions, the present status 

 of affairs would group the species and other allied forms of Amblema 



